Ellen Johnson Sirleaf, President of Liberia

Ellen Johnson Sirleaf, the first elected female head of state in Africa, has been president of Liberia since 2006.

The 73-year-old Harvard graduate has been nicknamed Liberia's Iron Lady for her political resilience and tough reputation. She, together with Leymah Gbowee of Liberia and Tawakel Karman of Yemen, was awarded the 2011 Nobel Peace Prize, in recognition of her efforts to further women's rights.

In 2010, Newsweek listed her as one of the ten best leaders in the world and Time magazine counted her among the top ten global female leaders. That same year, The Economist called her "arguably the best president the country has ever had."